This invention generally relates to a technology for fusing variable portions of a print medium as it passes through a fuser assembly of an electrophotographic device.
FIG. 1 shows a printer 100. More specifically, the printer is a xe2x80x9claser printer,xe2x80x9d which is a type of printer that utilizes a laser beam to produce an image on a photoconductive drum (which is known as the xe2x80x9cphotoreceptorxe2x80x9d). The light of the laser alters the electrical charge on the drum wherever it hits. The drum is then rolled through a reservoir of toner, which is picked up by the charged portions of the drum. Finally, the toner is transferred to the paper through a combination of heat and pressure. This is also the way copy machines work.
Because an electrophotographic process is used to print, laser printers may be generically called xe2x80x9celectrophotographic printers.xe2x80x9d In addition to the laser printer, there are two other types of printers that fall under the generic category of electrophotographic printers. However, they do not use lasers at all. One category uses an array of LEDs to expose the drum, and the other category uses LCDs. Both of these types of printers may be called xe2x80x9clight-array printers.xe2x80x9d Once the drum is charged, however, all electrophotographic printers (including laser and light-array printers) operate the same.
In conventional electrophotographic printers, a transfer unit cooperating with the photoconductive drum deposits toner onto the print medium, which is then cured or otherwise affixed to the print medium by a heated fuser assembly. An example of a print medium is paper, transparencies, envelopes, and the like.
Photocopier
Conceptually, the print engine in a laser printer is substantially identical to the print engine used in electrophotographic copying machines (i.e., xe2x80x9cphotocopiersxe2x80x9d). The fundamental difference between the two is the source of the image to be printed.
In the case of a copier, an original is illuminated by a high-intensity light and the image from the illuminated original is focused onto the photoreceptor. In the case of a laser printer, control circuitry is used to turn a laser beam on and off as it sweeps a raster pattern over the surface of the photoreceptor to directly create the image to be reproduced. Once the electrostatic image is created on the photoreceptor, the principle of operation of a laser printer and a photocopier are identical.
Unless expressly stated otherwise, references herein to the operation of an electrophotographic printer apply to the operation of an electrophotographic copier. Furthermore, examples of an xe2x80x9celectrophotographic devicexe2x80x9d include an electrophotographic printer (either laser or light-array) and an electrophotographic copier.
The fundamentals of electrophotographic devices are well known to those of ordinary skill in the art.
Fuser Assembly
The purpose of a typical fuser assembly (i.e., xe2x80x9cfuserxe2x80x9d) of a printer is to permanently affix the toner on the paper to the paper. Typically, the fuser heats the paper and the toner thereon as the paper passes through. The heat melts the toner onto the paper. By this process, a so-called hardcopy of an electronic document (xe2x80x9csoftcopyxe2x80x9d) is generated.
FIGS. 2A and 2B show two views of a conventional fuser 200. Such a fuser is typically formed from a heated roller 202 having a heated compressible surface 202a and a compression roller 204, which is urged against the heated compressible surface. A print medium 206 (such as a piece of paper or any other form of sheet medium) bearing the developed image of toner (not shown) is passed between the heated roller 202 and the compression roller 204. The heated roller 202 is, for example, made of a heat-conductive material, such as an aluminum tube coated with a layer of a heat-durable resin and is fitted with an internal built-in heater.
Alone or in combination with other rollers (not shown), the pair of rollers 202 and 204 may pull the print medium through the fuser 200. Alternatively, other rollers may provide the main locomotion to send the print medium through the fuser. Any device used to move the print medium through the fuser may be called a xe2x80x9cmedium-transporter.xe2x80x9d
In FIG. 2A, the print medium 206 travels vertically from bottom to top. In FIG. 2B, the print medium 206 travels horizontally from left to right. The print medium 206 travels from an unfused condition to a fused condition. In FIGS. 2A and 2B, area 206a is a portion of the print medium that has yet to pass through the fuser; thus, the toner in area 206a is unheated and unaffixed to the print medium. Area 206b is a portion of the print medium that has already passed through the fuser; thus, the toner in area 206b is heated and affixed to the print medium.
Notice, in FIG. 2A, that the rollers (of which only heated roller 202 is visible) extend across the full width of the print medium 206. The entire breadth of the print medium 206 passes through the fuser 200. The width of a print medium is along the x-axis and the breadth is along the y-axis.
In a conventional fuser (with laterally unmovable rollers such as fuser 200 of FIGS. 2A and 2B), the fuser is xe2x80x9conxe2x80x9d (i.e., heated) while the print medium passes there through. Therefore, the medium is fused along its entire width and breadth.
More precisely, a print medium passing through a conventional fuser is fused along the entire width and breadth of the medium""s printable area. A small unusable border (e.g., eighth of inch or less) around the perimeter of a print medium is common. In describing the background and this present invention, this unprintable perimeter is ignored.
Notice also that the rollers 202 and 204 do not move laterally relative to the print medium. Lateral movement of the fuser is movement along the x- or y-axes of the medium. Although the print medium 206 passes through the fuser, no part of the fuser moves laterally across the print medium.
The roller configuration shown in FIGS. 2A-2B is one example of a conventional fuser. Another example includes a fuser used for duplex printing. Such a fuser may include two heated rollers (one for each side of a page). Of course, those of ordinary skill in the art understand and appreciate that there are other roller configurations in a conventional fuser.
When fusing a page, a conventional fuser is either on or off. Without the ability to control where and when the fusing occurs, print media such as envelopes with cellophane windows, pages with special inks, adhesive labels, and the like cannot be printed because the heat of the fuser may cause them to melt or degrade. Conventional fusers can only fuse along the entire width and breadth of a page.
Described herein is a technology for fusing portions of a print medium as it passes through a fuser assembly of an electrophotographic device, such as a laser printer. An implementation, described herein, of the claimed invention includes a fuser of an electrophotographic device that can selectively fuse portions of a print medium passing through the fuser. Rather than fusing the entire width and breadth of a print medium passing through the fuser, an implementation, described herein, of the claimed invention fuses selected portions of the normal printable area of the print medium.
This summary itself is not intended to limit the scope of this patent. For a better understanding of the present invention, please see the following detailed description and appending claims, taken in conjunction with the accompanying drawings. The scope of the present invention is pointed out in the appending claims.